Process for producing pigment titanates



Patented JulylS, i939 I 2,166,22l

UNITED STATES PATENT OFFICE raooass rog l izglgt i cgq menmn'r Gordon 1). Patterson, Wilmington, Del., asslgnor to E, I. du Pont de Nemours & Company, Wilmington, DeL, a corporation of Delaware No Drawing. Application June 29,1937,

Serial No.150,968

12 Claims. (Cl. 23-51) This invention relates to a process for producthe objects of my invention to provide a process ing titanates, and more particularly to the proaffording greater latitude of control over themduction of water-insoluble titanates suitable for volved reaction, the use of lower and wider range use as pigments, g reaction temperatures, and avoidance of the ne- 5 Metal titanates can be prepared by calcining cessity of resort to chloride catalysts use. Other 5 mixtures of a titanium compound with the oxyand further objects and advantages of the invengen compounds of other metals. In. known proction will become apparent as the ensuing descripesses, however, high temperatures, in the vicinity tion proceeds.

of the fusion point of the reactants, must be em- In its broadest adaptation, the invention con-'- 'played to cause the reaction to go to substantial templates producing a substantially water-insol- 10 completion. High temperatures, particularly uble titanate pigment by reacting, under elethose of the order at which sintering or melting vated temperature conditionsand in the presence of thereacting components occurs, induce undeof water v p 01' Steam, titanium oxide with a sirable grit formation, rendering the resultant tibasic metal compounchwhereby the substantially 5 tanate unsuitable for pigmentary purposes. Tiinsoluble titanate pigment isforrned and the 'retanate production through employment of relaaction proceeds at a temperature very much betively low reaction temperatures and at which no low that at whic the reacting co p s would sintering or fusion components occurs, is of esotherwise react were not'the steam present. Varsential importanceinhigh-qualitypigment-titanious forms of hydrated or dehydrated titanium ate production. I I Oxide y be s J In an attempt to obviate the necessity of high In a more fic preferred e t, temperature employment, the use of chloride catthe invention comprises calcining an intimatealysts has been suggested for titanate producmixture of an oxygen compound of titanium, such tion. However, this type of catalyst is or such as a hydrated oxide obtained by the hydrolysis of nature that. it detrimentally aflects thev pigmena titanium sulfate or other salt solution, and an tary properties, such as texture and color, of the" other oxygen-metal compound, such as barium titanate produced. In addition, chloride catacarbonate, at a temperature not to exceed sublyst use necessitates resort to very narrow and stantially 1050 C. and preferably within a range undesirably close control over calcination tem- .01 from about 700 C. to about 975 Q. in the presperatures, in order to obtain a salable product ence of steam. Hydrated titanium oxides preand to avoid the bad effects arising by reason of pared by hydrolysis oi! titanium salt solutions over or under-treatment, or of incomplete 'reaccontain varying minor amounts of firmly held or tion. In addition, the resultant product 'will combined acid which is preferably removedby contain a relatively large "amount or water-soluneutralization and washing.

ble materials, 1. e of the order of 0.5% or more, In one practical embodiment of my invention,

' such as soluble salts, including some 0.15% or Irilrst prepare for calcination an intimate mixe more of combined chlorine. These water-soluble ture o1 titanium oxide and barium carbonate by. materials in the pigment are undesirable because any conventional method, such as dry mixing, of their relation to stability characteristics of the dry disintegration, mixing in the form of a water titanate when used in coating compositions. An slurry, ball milling, colloid milling, etc. Preferadded disadvantage of chloride catalyst presence ably, I ball mill a water slurry of the two comduring calcinationis the fact that the titanate ponents. I then remove the water from the ball particles become cemented together as relatively mill slurry and subject the resultant mixture to large, agglomerates, the latter making their apcalcination at atemperature ranging from about pearance' in the finished product inthe form of 750 C. to about 975 C. in the presence of steam deleterious g'rit. A further. objection 'to chloand for a time period suilloient to cause the reac- .ride catalyst use is corrosionoi equipment. tion to go to substantial completion. The;re- I haveiiound that these as well as other diflisulta'nt product, i. e., barium titanate, exhibits culties in prior titanate pigment production may highly improved pigmentary properties, including 9 eflectively'o'vercome; Accordingly, it is among excellenttinting strength, color and texture, and I ry and filtered out.

containsrelatively low and minor amounts of water-soluble material (less than 0.2%), while the chlorine. content thereoiis practically nil, representing only such impurities as may be present in' the raw material, amounting not to exceed about 0.05% calculated as chlorine.

In order that the invention may be more clearly understood, the following specific example is given, which is merely illustrative in character, and in no wise in limitation of the. underlying concepts of my invention:

A hydrated titanium dioxide was prepared by the hydrolysis of a titanium sulfate solution, followed by removal of residual sulfuric acid by neu-. tralization and washing. An amount of this hydrate corresponding to 100 parts T102 and 246 parts by weight of barium carbonate (1:1 melee ular proportion) was ball-milled in a water slur The intimate mixture ob tained wasthen calcined for one hour at 950 C. in a suitable calciner, steam being admitted at such rate as to maintain an atmosphere of nearly 100% water vapor in the calciner.

The resulting barium 'titanate was a finely-divided, white powder of good color and brightness;

possessing a tinting strength of 208, an increase of about 10% over a tinting strength of 188 in a barium titanate made with a chloride catalyst under the same conditions; its texture was equal to that of a commercial, finely-ground lithopone.

The above example illustrates a general method for the synthesis of metal titanates and demon-- strates the advantages which are obtained by my,

novel process. The process is equally applicable to the preparation of other white titanate pig-- ments of metals of the second group of the periodic arrangement of the elements, such as those of magnesium, calcium, strontium, zinc and cadmium, and particularly to alkaline earth metal tages of substantially complete reaction and increased tinctorial power are possible in the preparation of tinted or colored pigments comprising the titanates of metals such as lead, manganese, iron, cobalt, nickel, etc. A-wide'range of tints and colors is also possible by preparing mixed titanates in which the basic oxides combined with titanium oxide consist ofa mixture of metal oxides one of which forms a white titanate and the other a colored titanate. Furthermore, the process is also applicable to preparations in which another acidic oxide may replace a portion of the titanium oxide in the composition.

The tinting strength, color and texture determinations set forth in thepreceding example were determined in accordance with methods. commonly used for pigment testing. The method for tinting strength determination which was used is found described in Physical and Chemical Examination of Paints, Varnishes', Lacquers. and

Colors", eighth edition, January 1, 1937, by Henry A. Gardner, pages 83, 84 and 85, under the headving Tinting Strength of White Pigments-Du Pont Method.

The texture test used is essentially thetsame as that described on pages 511 and 512 of the same reference and designated,

- barium oxide.

TABLE I l5 Eflect of steam on calcination of barium titanate tinting strength Calcination temperature ag An additional beneficial effect which steam employment exerts in my invention is that with respect to effecting substantial completion of the reaction. In a typical barium titanate pigment preparation, such as illustrated in the above example, the unreacted barium content expressed as barium oxide, was 0.6%, whereas a comparable product made using a chloride catalyst in the .absence of steam contained 2.5% unreacted 35 A further desirable and beneficial efiect accruing as a result of steamemployment in my invention is that concerning the highly improved texture of the titanate product obtained. The following comparative table illustrates this outstanding feature of my invention:

TABLE II Texture of barium titanate (untreated alter .45 calcmation) Chloride Calcination temperature catalyst Gradings were made against a series of standards. A minimum of onev point is a significant difference. The higher the numerical'value, the finer the texture.

The fact that optimum texture is obtainable over a wide range of temperatures by steamcalcination in comparison with the more limited temperature range for other methods is obviously of considerable advantage, because it permits greater latitude'in control-of operations; Inas- 65 much as commercial success of pigments depends on cost, as well as pigment properties, texture fine enough to avoid the necessity of additional grinding is important.

The effect which the use of steam has upon reduction of the water-soluble content of titanate pigments prepared in accordance with my invention, as well as on chlorine content is shown by the following table:

. TAsLnlII Water-soluble and chlorine'content of barium titanates untreated after calcination Thus, it will be seen that lily-invention provides for the production of relatively pure and improved titanate pigments, the components of which are more completely reacted, at lower calcination temperatures. Additionally, the titanates obtainable exhibit improved pigment properties, particularly in regard to tinting strength,

texture, and color, and have improved paint properties due to reduction in water-soluble content, 1. e., to below 0.2% by. weight, as well asreduction of 'watersoluble chloride content, 1. e., to below 0.05% by weight (calculated as chlorine). Salts such as barium chloride, which are necessary during ordinary catalytic calcination, but eliminated by my invention, act as fritting agents, tending to bond the particles together and form large undesirable aggregates which induce undesirable grit formation in the ultimate pigment. Consequently, in contrast to titanates made at higher temperatures or in the'presence of chlorine catalysts, my novel, pigments are of fine, uniform particlesize, of excellent texture, free from grit,

' and, without further processing, are suitable for many purposes.

While specific reaction temperatures have been exemplified, it will be understood that the temperatures employable will largely depend upon the chemical nature .of the metalto be combined with the titanium in making up the ultimate titanate. In some instances, the use of a temperature as low as 450 C. in; the presence of steam will be found sufficient. In other instances, such 'as in the formation of alkaline earth metal titanates temperatures of the order of substantially 800-900 C. and the use of steam will usually. sufllce, though in the. absence of steam, much higher'temperatures will berequired to insure the same degree of completion of titanate formation. In the production of my novel titanates,

however, I prefer to insure a high quality both of texture and tinting strength by maintaining a reaction temperature not in excess of about 1050 0., and preferablybelow about 975 0., in the presence of steam. Pigments obtained at such low temperatures possess decided advantages in respect to physical form. overtitanates obtained by employment of substantially higher temperatures. When temperatures above about 1000' C. are employed, undesirable effects upon the physical characeristics of the titanate, such as tinting strength, color,'texture, etc.,-'begin to appear,

while above about 1050* C. these adverse effects become somewhat pronounced. Accordingly in the preferred adaptation of my invention, tem- .peratures below 975 C. are employed, in order R that a product of optimum pigment properties maybe obtained.

In the practice of my invention, I'prefera bly Qemploy an atmosphere consisting of straight steam. However, the amountof steam ,so employed is subject to variance within relatively wide limits. Very'good results are obtained with an atmosphere containing 50% by volume of steam. The eilects and benefits of steam use are evident even when an amount as low as 25% by volume is employed, but for optimum benefits under the invention I preferto use higher percentages. In

the practical a'daptation'of my invention, however, the; presence of as little as 10% by volume of steam appearsto exert no significant advantage over calcination in the absence of steam;

While specific titanates have been exemplified,

the invention has general application to the production of all types of substantially water-insoluble titanate pigments, including mixed titanates. By "titanate pigments I refer to a finely-divided solid having pigment properties, comprising one or more metal titanates and containing not less than. 10 per cent by weight of chemically combined titanium oxide. Specifically, the term "titanate" or ."metaltitanate", here and in the appended claims, embraces any salt of titanic acid such as 9. meta titanate or an ortho titanate,

or mixtures of such salts, and has particular reference to simple titanates comprising a chemical combination'of an oxide of titanium and an oxide of a metal other thantitanium, as well as to mixed metal titanates comprising a chemical combination of an oxide of titanium with the oxides of two or more metals other than titanium. These titanates are obtained by reacting in an atmosphere of steam intimate mixtures of acidic and basic oxides, i. e., an oxygen compound of titanium with an oxygen-metal compound other than titanium, such as an oxide or any other compound or substance adapted to yield an oxide during the reaction, such as a carbonate, hydroxide, or peroxide. Preferably, the acidic oxide includes not less than about 25%molar equivalent of titanium oxide and not more than about 10% molar equivalent of an oxide which produces a water-soluble pigmenting component on calwater-soluble pigmenting component below 10% by weight of the total pigment.

' It will be seen that titanate production from alkaline earth metals, which produce whitetitanates, as well as from theheavy metals which form more or less colored titanates, is contemplated. When the alkaline earth oxygen-metal compounds are employed, it will be found that my process yields titanates which are highly improved'in whiteness and better and superior in this respect than .titanates prepared by known processes, those prepared by my process being on the blue rather than-on the yellow side. This, of course; is-a very desirable property in a white pigment. -In particular, production of titanates containing one or more of the following metals is thus contemplated, namely, magnesium, calcium, strontium, barium, zinc, cadmium, lead,

cination; Normally it is preferable to keep the manganese, iron,cobalt and nickel. The oxides of these metals'may. be employed in the reaction with the oxygen compound of titanium, or other compounds of such metals, including the hydroxides, carbonates, or peroxides, or any salt of these metals adapted to decompose into the' reacjointly heated with titanium in the presence of steam to iorm mixed titanate pigments. Accordingly, the term oxygen-metal compoun here and in the appended claims, includes metal compounds which are capable of forming reactive oxides by thermal decomposition in the process of titanate formation, such as, for example, oxides, carbonates, hydroxides, or peroxides oi the metals mentioned.

I claim as my invention:

1. A process for producing substantially chlorine-i'ree, water-insoluble titanate pigments comprising reacting under elevated temperature conditions an acidic titanium oxide with a basic oxygen-metal compound from the group consisting of oxides, carbonates, hydroxides and peroxides, while maintaining the reactants at a temperature of at least 450 C. and not to exceed 1050 C. and in an atmosphere of at least 25% by volume of steam.

2. A process ior producing substantially chlorlne-free insoluble metal titanates comprising calcining an intimate mixture of titanium oxide with an oxygen-metal compound from the group consisting of oxides, carbonates, hydroxides and peroxides, while maintaining the reactantsat a temperature ranging from substantially woo-975 C. and in an atmosphere of at least 25% by volume of steam.

3. A process for producing a chlorine-tree, water-insoluble titanate pigment comprising subjecting an intimate mixture or a titanium oxide and an oxygen-metai compound selected from the group consisting of oxides, carbonates, hydroxides and peroxides to calcination at a temperature of at least 450C. and not exceeding 1050" C. and in an atmosphere 01' at least 25% by volume of steam.

4. The process of claim 3 in which the calcination is carried out at a temperature below thesintering point of the reaction mixture.

5. A process for producing a substantially chlorine-Iree pigment titanate comprising heating to a temperature between substantially 750 and 975 C. an intimate mixture of titanium dioxide 7 and a carbonate of a metal from the group consisting oi magnesium and the alkaline earth metals,, and conducting said reaction in an atmosphere of at least 25% by volume of steam.

6. A process for producing substantially chlorine-iree pigment barium titanates, comprising heating an intimate mixture of titanium dioxide and -barium carbonate in equimolecular propor-. tions to a temperature about 950 C., while maintaining said reactants during said heating in an atmosphereoi at least 25% by volume of steam.

droxides and peroxides.

8, A process for producing a substantially chlorine-iree, water-insoluble titanate pigment, comprising reacting at a temperature ranging from 750 to 975 C., and in an atmosphere containing at least 25% water vapor by volume, an intimate' mixture of an oxide of titanium with an oxygenmetal compound from the group consisting of oxides, carbonates, hydroxides and peroxides.

9. A process for producing a substantially chlorine-free, water-insoluble titanate pigment, comprising reacting at an elevated calcination tem-' perature not to exceed 1050 C., and in an atmosphere containing at least 50% of water vapor by volume, an intimate mixture of an oxide of titanium with an oxygen-metal compound from the group consisting of oxides, carbonates, hydroxides and peroxides.

10. A process for producing a chlorine-free, water-insoluble titanate pigment, comprising reacting an intimate mixture of an oxide of titanium with an oxygen-metal compound from the group consisting of oxides, carbonates, hydroxides and peroxides, while maintaining the reactants at a temperature of at least 450 C. and not in excess of 1050 C., and in an atmosphere of at least by volume of steam.

11. A process for producing a substantially chlorine-free, water-insoluble pigment titanate,

' comprising subjecting an intimate mixture of ti!- tanium oxide and the oxide of a metal, the titanate 01 which is water-insoluble, to calcination in at atmosphere of at least 25% by volume of steam, and at a temperature of at least 450 C.

and not exceeding 1050 C.

12.A process for producing a substantially chlorine-free, water-insoluble pigment titanate, comprising heating to a temperature between substantially 750 and 950 C. an intimate mixture of titanium oxide and an alkaline earth oxygenmetal compound from the group consisting of oxides, carbonates, hydroxides and peroxides, while maintaining the reactants in an atmosphere of at least 25% by volume of steam.

GORDON D. PATTERSON. 

